The "standard" transfer modes in use over the parallel
port are "defined" by a document called IEEE 1284. It
really just codifies existing practice and documents protocols (and
variations on protocols) that have been in common use for quite
some time.

The original definitions of which pin did what were set out by
Centronics Data Computer Corporation, but only the printer-side
interface signals were specified.

By the early 1980s, IBM's host-side implementation had become the
most widely used. New printers emerged that claimed Centronics
compatibility, but although compatible with Centronics they
differed from one another in a number of ways.

As a result of this, when IEEE 1284 was published in 1994, all that
it could really do was document the various protocols that are used
for printers (there are about six variations on a theme).

In addition to the protocol used to talk to Centronics-compatible
printers, IEEE 1284 defined other protocols that are used for
unidirectional peripheral-to-host transfers (reverse nibble and
reverse byte) and for fast bidirectional transfers (ECP and
EPP).